In general, in a simulation experiment corresponding to a predetermined altitude, a mechanical vacuum pump may be used to reduce a pressure inside a vacuum container. When the inside pressure reaches a preset altitude, the mechanical vacuum pump may be turned off to conduct the experiment. In this case, the experiment may be conducted by reducing the pressure using the mechanical vacuum pump in a pressure range corresponding to the altitude below 18 kilometers (km), for example, from atmospheric pressure to 7000 pascals (Pa) or from atmospheric pressure to 50 Torr until the pressure reaches a preset pressure, and turning off a blocking valve connecting the mechanical vacuum pump and the vacuum container to maintain the pressure.
In a simulation experiment corresponding to a higher altitude environment, a lower pressure range than the aforementioned pressure range may be applied. In this case, even when the blocking valve is turned off, a designed pressure may not be maintained due to a degassing phenomenon and a leakage phenomenon that may occur in the vacuum container. Accordingly, there is a desire for a system of maintaining a predetermined altitude environment during a predetermined period of time.